Disc drives are digital data storage devices which store and retrieve large amounts of user data in a fast and efficient manner. The data are magnetically recorded on the surfaces of one or more rigid data storage discs. The discs are affixed to a spindle motor for rotation at a constant high speed. The discs and spindle motor are commonly referred to as a disc stack.
The disc stack is accessed by an array of vertically aligned data transducing heads which are controllably positioned by an actuator assembly. Each head typically includes electromagnetic transducer read and write elements which are carried on an air bearing slider. The slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly each head in a closely spaced relationship to the disc surface.
In order to maintain the proper flying relationship between the heads and the discs, the heads are attached to and supported by flexible suspension assemblies (flexures). An actuator motor (typically a voice coil motor, VCM) rotates the actuator assembly to cause the heads to move across the disc recording surfaces. The actuator assembly is also referred to as a head stack assembly (HSA). Both the disc stack and the HSA are mounted to and supported by a rigid base deck of the drive.
During normal operation of the disc drive, the heads are moved over data storage portions of the discs to write data to and read data from the discs as directed by the host device. When not in use, the heads are moved to a parked position such as on texturized landing zones near the inner diameter (ID) of the discs. A latch typically secures the actuator when the heads are in the parked position to prevent inadvertent movement of the heads out onto the data storage portions of the discs as a result of the application of a non-operational mechanical shock to the drive.
Direct contact between the heads and the data storage portions of the discs is usually undesired since damage can occur to the heads and/or discs if the heads come to rest against the data storage portions while the discs are in a nonrotating state. Moreover, if the stiction forces between the heads and discs are too great, the spindle motor may not be able to generate sufficient torque during a subsequent initialization operation to break the discs free, resulting in a catastrophic failure of the drive.
Accordingly, a typical disc drive is configured to retract the heads to the parked position when the disc drive enters a deactivated state, such as in response to a sleep command or in response to loss of power to the drive. The retraction of the heads typically takes place while the discs are decelerating to rest and thus the drive attempts to complete the movement of the heads to the parked position before the velocity of the discs drops to a level where the heads are no longer aerodynamically supported over the disc surfaces.
A variety of factors can cause the retraction operation to not be completed successfully, resulting in the landing of the heads onto the data storage portions of the discs. This often occurs during drive development, but can also happen during field use. If a head landing on a data storage portion of a disc does not result in catastrophic failure of the drive (due to the inability to subsequently spin-up the discs), the occurrence of data zone landings may go undetected, but nevertheless may degrade the reliability of the drive.
One way the occurrence of data zone landings can be indirectly detected is when sufficient amounts of data have been corrupted due to prior landings. This approach can take a long time to detect because there may be only a small degradation of the discs, because error correction code (ECC) techniques may mask the problem, or because the testing process for the disc drive may not return to the affected data zone for a long time.
Another way to detect data zone landings is to open the drive visually inspect for evidence of improper landing events. These indirect methods identify the occurrence of data zone landings much too late in the process.
There is therefore a need for improvements in the art directed to detecting when a disc drive head improperly lands in a data zone of a disc surface.